This invention relates generally to the field of jet drop recording and, more particularly, to jet drop recorders of the type shown in U.S. Pat. No. 3,373,433, issued Mar. 12, 1968, to Sweet et al, and U.S. Pat. No. 3,701,998, issued Oct. 31, 1971, to Mathis. In recorders of this type, one or more orifices receive an electrically conductive recording fluid, such as a water base ink, from a pressurized fluid supply manifold and eject the recording fluid in parallel streams of ink drops. The production of drops is typically facilitated by mechanical stimulation of the orifice structure or of the recording fluid in the manifold. Graphic reproduction is accomplished by selectively charging and deflecting the drops in each of the streams and, thereafter, depositing at least some of the drops on a print medium, such as a moving web of paper. The drops which are not deposited on the moving web are caught by an appropriately positioned catcher.
Typically, the drops in each of the streams are deflected by a deflection field which is generated by a deflection electrode having a deflection potential impressed thereon. The catcher structure may typically be grounded and may be positioned on the opposite side of the stream or streams from the deflection electrode. Various deflection electrode configurations have been used. Where the orifices are positioned in two parallel rows, a thin ribbon-like electrode structure which extends between the rows of drop streams may be used. Positioned outwardly from the deflection ribbon are two catchers. The deflection potential applied to the ribbon will be of the same polarity as the charge carried by the charged drops in the drop streams. The charged drops will, therefore, be deflected outwardly away from the deflection ribbon and toward the catchers.
The environment in which ink jet printers of the type described above operate may present problems with respect to electrical isolation of the ink jet printer component parts. If the printing is accomplished on a rapidly moving web of paper, as is typical, the movement of the paper will result in air turbulence in the vicinity of the deflection ribbon and catchers and this air may have a high particle content. Particles both from the paper stock and other contaminant sources may therefore find their way into the printer. When this occurs, the deflection ribbon, bearing a deflection potential of approximately-1100 volts, may arc or short to other printer components which are operating at differing electrical potentials.
Typically, jet printers of this type have printed with uncharged drops and deflected charged drops to the catchers. If the deflection ribbon is grounded and the deflection field collapses, however, even the drops which are intended to be deflected to the catchers will pass between the deflection ribbon and the catchers and will be deposited on the print medium. It can be seen, therefore, that the shorting of the deflection ribbon may result in a substantial quantity of ink being deposited upon the print medium. In the case of a paper print web, this ink deposit may flood the web, dampening it to the point where the web will break. Should this occur, a substantial period of time will be required for cleanup and restarting operations. It has been common practice, therefore, for the printers to be shut down automatically at the initial detection of a printer short to prevent such situations. In a relatively dirty operating environment, bar shorts may occur frequently, causing the jet printer to be shut down an inordinate number of times and thereby reducing operating efficiency.